1. Technical Field
The present invention relates to an apparatus and a method for controlling an air supply into a fuel cell stack, and more particularly, to an apparatus and a method for controlling an air supply into a fuel cell stack capable of rapidly reducing an air supply up to a required flow rate when it is required to suddenly reduce a flow rate of air supplied to the fuel cell stack for a sudden reduction in vehicle power, etc., in a pressurized operation condition.
2. Description of the Related Art
A method of operating a fuel cell system applied for fuel cell vehicles is classified into an ambient pressure type and a variable pressure type. In each of the operating methods, an operating pressure of the fuel cell stack is a factor that affects the overall performance of the fuel cell vehicle. Among the fuel cell systems, the ambient pressure fuel cell system uses an air blower which does not require a substantial amount of power to supply ambient pressure air to a cathode of the fuel cell. Considering that power of peripheral devices for supplying air is supplied from the fuel cell stack, the ambient pressure fuel cell system may reduce the power consumption of the peripheral devices. On the other hand, considering that as the operating pressure of the fuel cell stack increases, the efficiency of the fuel cell increases, the low pressure of the fuel cell system may reduce the power density of the fuel cell stack.
Accordingly, the variable pressure fuel cell system has been developed which operates at a substantially low pressure to minimize parasitic power in a low power section to improve the efficiency of the fuel cell system and operates at a substantially high pressure in a high output section to improve the performance of the fuel cell system. The variable pressure fuel cell system uses an air compressor to supply higher-pressure air than the ambient pressure to the cathode and has a separate back pressure control valve mounted within a pipe for gas passing through the fuel cell stack to adjust a pressure of gas supplied to the fuel cell stack.
In response to determining that the state of the fuel cell stack is dry or when high power is required such as high temperature, high output, and a high load, the variable pressure fuel cell system is required to be operated in a high air pressure state. When the vehicle power is suddenly reduced under the operation condition, a vehicle controller is configured to suddenly reduce a speed of the air compressor to suddenly reduce the flow rate of air, thereby preventing the fuel cell stack from drying due to the excessive supply of air.
When the pressure formed by the air previously supplied to the fuel cell during the above process is not reduced (e.g., is maintained or is increased), the air compressor may be operated in a surge region while the flow rate of the air compressor is suddenly reduced. When the air compressor is operated in the surge region, the pressure and the flow rate unstably appear within a cathode pipe. Further, when the air compressor is repeatedly operated in the surge region, the instability of the pressure and the flow rate has an adverse effect on long-term durability of the air compressor and the fuel cell stack and thus the power of the fuel cell stack may be unstable.